1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method suitable for manufacturing a thin film transistor (hereinafter abbreviated to a “TFT”) substrate used in for example a liquid crystal display device or an organic electroluminescent device, and a display device including a semiconductor film manufactured by the method.
2. Description of the Related Art
When a high-value-added active matrix type liquid crystal display device referred to as a system liquid crystal, an organic electroluminescent display device (hereinafter referred to as an “organic EL display device”) using an organic electroluminescent element (hereinafter referred to as an “organic EL element”), or the like is formed, a TFT substrate with crystalline silicon is generally used. This TFT substrate is generally made by forming an amorphous semiconductor film or a polycrystalline semiconductor film with a relatively small particle diameter on a substrate, performing an annealing process by irradiating the semiconductor film with a laser beam, and then forming a TFT as a driving element.
A low-cost and high-stability semiconductor laser may be used as a light source of a laser annealing apparatus (see Japanese Patent Laid-Open No. 2003-332235, for example). However, when a semiconductor laser is used, because of very small size of a beam spot, a scanning time per unit area is increased, thus inviting a decrease in productivity, an increase in manufacturing cost, and the like. It is accordingly proposed for higher throughput in the annealing process that a plurality of lasers are arranged in proximity to each other, and a plurality of parts of an amorphous semiconductor film are irradiated with a plurality of laser beams to thereby shorten the scanning time and increase productivity (see Japanese Patent Laid-Open No. 2004-153150, for example).
FIG. 14 shows an example of a pattern in which a substrate 310 is irradiated with a plurality of laser beams LB, for example three laser beams LB. On the substrate 310, a semiconductor film 320, for example, is formed, and three irradiation areas 311A, 311B, and 311C are set. Each of the laser beams LB is assigned to one of the three irradiation areas 311A, 311B, and 311C, and the laser beams LB are applied to the corresponding irradiation areas 311A, 311B, and 311C while scanned continuously in lines.